Blood pressure indicator and noise

ABSTRACT

An electronic blood pressure indicator for use with conventional inflatable arm cuff apparatus and a mercury or aneroid manometer, comprising a microphone for translation of arterial blood flow sounds into electrical signals, a narrow bandpass amplifier circuit which filters extraneous frequencies and amplifies a narrow band of low frequencies containing essential arterial blood flow information, a discriminator which senses signal strength and passes only signals exceeding a predetermined value, a pulse generator which provides a pulse output corresponding to blood flow pulses passed by the discriminator, the pulse generator cooperating with switch means to drive an indicator to provide a visual indication of the arterial blood flow sounds, and a dual lockout circuit which blocks incoming signals and spurious pulses from the pulse generator.

ilnite States Patent iEglliet ai.

1151 dflifi [54] L001) PRESSURE INDICATOR AND 3,171,292 3/1965 Pantle..12s/2.os R NOISE $13013 2:363 Vogt ..12s/2.05 A ,3 ,14 6 Young....l28/2.05 S [72] Inventors: g g i g 3,550,582 12/1970 Wilhelmson 128/205 A s H. Wilcox, Castle Rock, Colo. primary E i wflli 5 Kamm [73]Assignee: Parke, Davis & Company, Detroit, Mich. Attorney-Paul Paul [22]Filed: May 15, 1970 [57] ABSTRACT PP N05 37,543 An electronic bloodpressure indicator for use with conventional inflatable arm cuffapparatus and a mercury or aneroid [52] U 5 Cl 128/2 05 s 128/2 05 P128/2 05 M manometer, comprising a microphone for translation of arteri-ST 6 al blood flow sounds into electrical signals, a narrow bandpass I 5l 1 Int Cl sloz amplifier circuit which filters extraneous frequenciesand am- 58] i 2 05 P plifies a narrow band of low frequencies containingessential 128/2 05 S arterial blood flow information, a discriminatorwhich senses 2 d 5 signal strength and passes only signals exceeding apredetermined value, a pulse generator which provides a pulse output I56] References Cited corresponding to blood flow pulses passed by thediscriminator, the pulse generator cooperating with switch means toUNITED STATES PATENTS drive an indicator to provide a visual indicationof the arterial blood flow sounds, and a dual lockout circuit whichblocks ini 1 5 f coming signals and spurious pulses from the pulsegenerator. a1 ey 3,318,303 5/1967 Hammacher 128/205 S 9 Claims, 3Drawing Figures -E T3 E 16 1 1 1 E323 D1SCRIMINATOR z 'ig SWITCHINDICATOR v I I I7 I DUAL LOCKOUT I i UNREGULATED POWER SUPPLYPMENTBNR28 m2 INVENTORS, PAUL H. EGLI BY WARREN vv. BRENNER MARTIN H.WILC x W #W ATTORNEYS.

BLOOD PRESSURE INDICATOR AND NOISE BACKGROUND OF THE INVENTION 1. Fieldof the Invention This invention lies in the field of electronicsphygmomanometer apparatus and, more particularly, electronic bloodpressure detection and indicator apparatus.

2. Description of the Prior Art The art of measuring blood pressure hasbeen well developed by the medical profession, resulting in a standardand near-universal procedure for taking blood pressure measurements. Theprocedure involves inflating a rubber bladder in a cloth cuff encirclingthe patients arm, thus forming an occlusion opposing the arterial flowof blood, the blood being under pressure from the heart. When thebladder is inflated t a pressure sufficient to cut off the blood flowentirely, the pressure is slowly released until blood flow resumes inthe artery. As the pressure drops, a point is reached where thepulsating blood flow first pushes through the cuff, causing audio soundsnormally detectable with a stethoscope. At the point of first detection,where the decreasing bladder pressure is matched by the maximum, orsystolic blood pressure, the doctor skilled in auscultation can detectthe pulsatile flow in the artery, and determine the systolic pressure.As the cuff pressure is further reduced, the blood pulses generate aseries of distinct sounds audible with a stethoscope to persons withaverage hearing in an environment of normal background noise. Thefurther reduced cuff pressure at which the sounds fade away is thepressure which the skilled doctor detects as the diastolic pressure.Through long use of the stethoscope, this point in cuff pressure hasacquired an important clinical meaning. Although cuff pressure mustdecrease further beyond this point until completely unimpeded flowresults, it is this long used cuff pressure which is clinicallyimportant, and which any instrument must be capable of registering.

The disadvantages of the conventional stethoscope are that the operatoris required to make subjective detections of the sound of blood pulseswhich are faint and intermixed with ambiguous external noises, and thatthe detennination of the end points of the blood fiow pulse train issomewhat subjective and therefore subject to inaccuracy. To overcomethese disadvantages, electric sphygmomanometers have been devised,utilizing electronic to in cooperation with a microphone for amplifyingand detecting the auscultatory signals. However, such electronic deviceshave been subject to system design deficiencies, particularly inproviding the required sensitivity, avoiding inaccuracy caused by powersupply variations, proper filtering of electronic noise and extraneoussignals derived from muscle movements, efficient matching of theelectronic circuitry with the microphone, and the problems of powerconsumption, size and cost.

SUMMARY OF THE INVENTION It is an object of this invention to provide animproved electronic blood pressure indicator which will provide anindication of diastolic and systolic pressure, the indication being freeof background noises and extraneous body signals.

It is a further object of this invention to provide an electronic bloodpressure indicator which can be used with conventional sphygmomanometerequipment and which will operate with a constant sensitivity.

It is a further object of this invention to provide a blood pressureinstrument which clearly indicates blood flow signals and which preventsindication of unwanted signals derived from the patient as well asgenerated internally by the instrument.

It is a still further object of this invention to provide anoisediscriminating pulse amplifier adapted for blood pressureindication.

Accordingly, the invention provides a microphone sensor which isresistor-calibrated to provide a standardized output voltage; anamplifier which filters out signals outside of a narrow bandwidth of thedesired auscultatory signals; a discriminator circuit which establishesthe instrument sensitivity by selecting the passable signal amplitude; apulse generator comprised of opposite polarity transistors to produce apulse of uniform shape from the variable signal output of thediscriminator; a switch and indicator light driven by the pulsegenerator output and powered by an unregulated power supply; a duallockout circuit which locks out transmission of any signals to theindicator until a fixed period after a previous signal pulse; and adiode regulated power supply. In operation, the auscultatory signals aredetected by the microphone and fed into the amplifier, the amplitude ofthe signals is sensed by the discriminator which permits passage of thesignals from the time cuff pressure is at systolic pressure to the timethat it drops to diastolic pressure. After each pulse, the lockoutcircuit prevents any further indication for a period approaching thetime when the next blood pressure pulse is due to arrive.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing thesystem function of the different portions of the instrument.

FIG. 2 is a schematic diagram of the electronic circuitry of thepreferred embodiment.

FIG. 3 is a perspective view of the preferred form of microphoneassembly to be used with the instrument of this invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Referring now to FIG. 1, theauscultatory sounds caused by the pulsating blood flow are sensed by asensor 111, which transforms the sounds into electrical signals. Thesignals are coupled into the bandpass amplifier 12 which filtersextraneous signals and amplifies the desired signals in a narrowfrequency range of approximately 10 to 50 Hz. The significant sounds tobe detected from the occluded blood flow in the artery have a peakintensity at about 40 Hz. Any microphone capable of responding at thislow frequency would also produce signals from extraneous noise in thebackground, as well as from electromagnetic radiations produced byadjacent equipment, lights, etc. There is thus a requirement for a sharpfrequency cut off filter to provide filtering before and duringamplification of the electrical signal, as will be pointed out in moredetail hereinbelow. The signals generated by the microphone and coupledinto the amplifier are in the range of nanoamps or lower, and theamplifier accordingly must have a stable gain of several thousandswithout introducing appreciable noise which would result in ambiguoussignals.

The output of the amplifier 12 is coupled to the discriminator circuit13 which serves as the amplitude selecting component of the system,rejecting smaller level signals generated by extraneous noise. Thesignal level required to pass the discriminator is the design criterionwhich sets the sensitivity of the overall system.

The output from the discriminator 13 is coupled into a pulse generator14 which produces a pulse of uniform shape and amplitude to activateswitch 15. The signals passed from the discriminator are highly variablein both frequency and amplitude because of the irregularity of thearterial sounds during the course of the cuff pressure drop. Further,there is a considerable difference in signal strength from patient topatient depending upon the patients arm build and blood pressure. Thus,the pulse generator transforms these variable signals into standardizedsignals which contain the required information. The switch 15, driven bythe output of the pulse generator M, operates the indicator 16,preferably an incandescent light bulb, which provides the instrumentoutput. As will be noted hereinbelow, the light bulb constitutes thelargest drain on the battery power source, and it is accordinglyimportant to provide that it be turned on for the shortest possible timeconsistent with a clearly visible light pulse. Accordingly, the shape ofthe pulse from the pulse generator and the switching characteristics ofthe switch are important design features.

In practice, the light indicator 16, which provides signals representingthe blood flow sounds, will be used in cooperation with a conventionalpressure gauge marking, so that the operator can quickly and efficientlyread the systolic pressure when the light first starts to blink, andread the diastolic pressure when the light ceases to blink. For ananeroid pressure gauge the best position for the indicator is in thecenter of the radial dial, and for a manometer, it is best placedimmediately alongside the calibrations on the mercury column. Theindicator light may be of any conventional form, although the preferredembodiment incorporates an incandescent bulb having the advantages ofoperating on low voltage and being long lived.

Still referring to FIG. 1, a dual lockout circuit 17 is indicated, whichis activated by the output from the switch 15, and which controls theoperation of the pulse generator 14. The regulated power supply 18provides power to all of the circuitry except the indicator light 16,which is supplied by the battery or unregulated supply 19. Indicator 16is therefore subject to fading as the battery becomes exhausted.However, the user is assured of accurate readings so long as he can seethe flashing light, since the supply 18 will maintain sensitivity andaccuracy of the measurements with battery deterioration up to the pointwhere the indicator light is no longer visible.

Referring now to FIG. 3, the active element is a conventionalpiezoelectric crystal 21 such as a Rochelle salt or a ceramic bimorph.The crystal 21 is mounted from the bottom of the housing on cork orrubber pads 22 on opposite corners of the crystal 21. The pads aresuitably 0.03 inch thick and one-sixteenth inch wide, providing a stableplatform without unduly restricting the crystal from bending. On top ofthe crystal a light metal bridge 23 is rigidly attached to the twocorners opposite from the support pads, and extends up to a point at thecenter of the diaphragm 24. The front of the microphone housing is roundso that the diaphragm will have the symmetrical vibration pattern of acircular plate. The back of the microphone is made rectangular so thatthe rubber bladder within the cuff, which folds over the microphone,distributes the pressure evenly and holds the microphone into closecontact with the skin.

The microphone is designed to produce an output of about an order ofmagnitude larger than necessary to drive the amplifier. The desiredoutput is trimmed by inserting, in parallel with the microphone output,a selected resistor 25. The resistor 25 is chosen of a value to trim theeffective output voltage of the microphone to a standardized value.

Referring now to FIG. 2, the narrow bandpass amplifier component of thecircuitry is comprised of transistors 51, 52, 53, 54 and 55, withassociated circuitry. The filtering function is distributed throughoutthe amplifier. The intrinsic capacitor of the microphone in combinationwith resistor 42 provides a first low frequency rejection circuit.Additional low frequency filtering is accomplished by capacitor-resistorcombinations 41, 43 and 44 connected to the base terminals oftransistors 51, 53 and 54 respectively, and combination 45 connectedbetween ground and the emitter of transistor 55. High frequencyrejection is obtained by capacitor-resistor combinations 56, 57 and 58connected between ground and the collectors of transistors 51, 53 and 54respectively. These networks thus provide an effective narrow bandwidthof frequencies having a peak amplification occurring at approximately 25Hz, and providing adequate amplification at 40 Hz to detect the desiredarterial signals. The bandwidth is peaked at 25 Hz rather than 40 Hz toimprove the rejection of 60 Hz noise signals.

The signal is amplified by transistors 51, 53 and 54 and associatedcircuits acting in cascade. Transistor 52, in emitterfollowerconfiguration, acts to isolate transistor 51 from transistor 53.Transistor 55 provides additional power amplification. Amplifier voltagegain is established and maintained at a known value by holding the basebias voltage of transistors 51, 53 and 56 independent of batteryvoltage, and by the negative feedback provided by the high value emitterresistors of those transistors.

The discriminator circuit 13 is coupled to the output of the amplifierthrough capacitor 61, and is comprised of diode 62 and the base-emitterjunction of transistor 63. Both diode 62 and the base-emitter junctionof transistor 63 have forward bias, or tum-on voltages. The voltagecoupled through capacitor 61 must attain the magnitude of the twocombined tum-on voltages before signal current will flow into the baseof transistor 63. If the signal amplitude supplied through capacitor 61is less than the sum of the tum-on voltages of diode 62 and transistor63, no signal current flows into the base of transistor 63, andconsequently pulse generator 14 remains in its stable state. By thiscircuitry, amplitude selection is obtained, with the smaller level noisesignals and extraneous body signals being rejected. It is noted that theturn-on voltages of diode 61 and transistor 63 are uninfluenced bybattery voltage changes and vary negligibly within component productiontolerances.

The pulse generator 14 is comprised of transistors 63 and 64 andassociated elements, and operates in the following manner. Betweenpulses, transistors 63 and 64 are non-conducting, and the capacitor 73is discharged, having no voltage across it. When the signal exceeds thethreshold level and turns on transistor 63, a large current flowsthrough resistors 74 and 75 which are series connected between thecollector of transistor 63 and the power supply, developing a forwardbias voltage at the base of transistor 64, thus turning it on. Withtransistor 64 switched on, current is supplied to resistor 71,generating a positive voltage which is impressed across capacitor 73 andresistors 77 and 78 in series with diode 79. Capacitor 73 chargesexponentially through diode 79 to a voltage which is approximately thevoltage across resistor 71. During the rise in voltage across capacitor73 diode 80 is non-conducting, and the charging current flows throughresistor 77, adding to the current initially flowing through diode 62,thus providing a greater input to transistor 63 and driving it furtherinto an on condition. Since the output of transistor 63 is coupled tothe input of transistor 64, transistor 64 is also driven into a greateron condition, in turn increasing the input to transistor 63, and so on.Thus, transistors 63 and 64, through this regenerative action, arequickly driven into saturation and appear as essentially short circuits,with each supplying the driving current required by the other. Thiscondition is maintained so long as the current passing through resistor77 is sufficient to maintain saturation of transistor 63, and is afunction of the time constant by which capacitor 73 is charged. It isnoted that this time constant is determined solely by capacitor 73 andresistors 77 and 78, and not by the amplitude of the incoming signal.When capacitor 73 approaches its fully charged condition, the chargingcurrent tapers off and a reverse or degenerative process sets in,quickly taking both transistor 63 and 64 out of conduction and turningthem off, thus terminating the voltage pulse appearing across resistor71. Capacitor 73 at this time discharges rapidly through diode 80 andresistor 81, diode 79 being non-conducting during this discharge.

From the above, it is seen that pulse duration can be determined bydesign of capacitor 73 and resistors 77 and 78. Further, transistors 63and 64 are chosen as opposite polarity transistors, one being an NPN andthe other a PNP, so that both transistors can be in the off state duringthe relatively long period between pulses, thereby avoiding energy drainfrom the battery.

The indicator 72 is driven by an indicator switch 15, comprised oftransistors 91 and 92 in cascade. When the pulse generator delivers avoltage across resistor 71, the signal is transmitted through resistor93, turning on transistors 91 and 92. Transistor 92 is driven heavilyinto conduction, thereby effectively closing the circuit through thepower supply 94 and the indicator 72, for the duration of the pulsegenerator output.

Still referring to FIG. 2, the dual lockout circuitry 17 is comprised ofthe feedback loop from the collector of transistor 92 to the base oftransistor 63, comprising resistor 101, capacitor 102, and resistor 104in series, resistor 104 being tied to the base of transistor 106, thecollector of which is connected to the base of transistor 03. Diode 103is connected between ground and the node joining resistor 104 andcapacitor 102. Resistor 105 is connected between the base of transistor106 and ground. In operation, between output pulses capacitor 102 ischarged to appreciably the battery voltage. When an output pulse drivestransistor 92 into conduction, capacitor 102 discharges through resistor101, diode 103 and transistor 02 until the voltage across its terminalsapproaches zero. At the end of the output voltage pulse, transistor 92turns off again, impressing the battery voltage across capacitor 102.The capacitor 102 charges through resistors 101, 104 and 105, with thevoltage across resistor 105 appearing on the base of transistor 106,driving it into conduc tion. As transistor 100 is driven intoconduction, it clamps the base of transistor 63 appreciably to ground,disenabling it from passing any signals through to the output. Thus, thepulse generator will remain inactive as long as transistor 106 remainsin its conductive condition, which condition will be maintained for aduration set by the time constant of the charging path for capacitor102, i.e., capacitor 102, resistor 101, 104, and 105. When the chargingcurrent becomes insufficient to maintain transistor 106 in conduction,it switches to an off state, thereby enabling transistor 63 to passsignals which appear at its input.

The above described lockout circuit serves a dual function. The firstfunction is that of eliminating all extraneous signals other than theanticipated arterial sounds. As the approximate time period between suchauscultatory sounds is well known, the time constant of the lockoutcircuit can be designed to eliminate most extraneous signals which mightoccur between the desired arterial pulses. The second function of thelockout circuit relates to the power drain of the indicator light. Whenthe indicator light 72 is flashed on, it initially draws an appreciableamount of current as compared to the current load of the entire circuit.Consequently, the voltage source 94 will suffer a drop in voltage, whichdrop will cause a transient signal to be amplified through the circuit,thereby driving one or more of the transistors into saturation. Due tothe relatively large amount of capacitance in the circuit for frequencyselectivity purposes, the saturated transistors would not return totheir linear state until appreciably after the pulse, at which timeadditional undesired transients would be generated and result inmultiple lamp output flashes, with consequent user confusion andadditional battery drain.

Still referring to FIG. 2, the regulated power supply is comprised ofbattery 941, capacitors 111, 112 and 113, diodes 115, 116, 117 and 120,and resistors 118 and 119. Capacitor 113 provides the initial currentnecessary to drive indicator 72, which requires an initial current abouteight times the steady state current of the circuit. Capacitor 112,connected to battery means 941 through a diode 120 maintains an adequatepower supply for the amplifier stages during the indicator on period,when light 72 is loading down the battery. Capacitor 111 and resistor110, connected between capacitor 112 and ground, provide additionalfiltering of the power supply to transistors 51 and 53, the two mostsensitive amplifier stages. The series combination of diodes 115, 116and 117 in combination with resistor 119 provide an amplifier biasvoltage supply substantially independent of the battery voltage. Thisprovision of a stable bias voltage is combined with large value emitterresistors to render the instrument sensitivity relatively immune frombattery voltage variations and transistor production tolerances.

What is claimed is:

1. Blood pressure indicator apparatus for indicating the blood pressureof an individual by detecting auscultatory signals originating in theindividual, said blood pressure indicator apparatus comprising:

a. microphone transducer means, adapted to be placed against an arm ofsaid individual, for generating electrical signals representative ofblood flow sounds within said arm of said individual;

b. narrow bandpass amplifier means having input terminals connected tothe output terminals of said microphone transducer means for amplifyingsaid representative signals, having filter sections providing for theamplification only of a narrow bandwidth of low frequency signalscorresponding to the appreciable bandwidth of said blood flow signals;

c. discriminator means connected to and driven by said amplifier meansfor providing output responsive only to signal amplitudes greater than apredetermined amplitude;

. pulse generator means connected to and driven by said discriminatormeans for providing output pulses of fined amplitude and time durationresponsive to the output signals of said discriminator means;

e. indicator means for providing a visual output corresponding to theoutput pulses of said pulse generator means;

f. switch means connected to and driven by the output of said pulsegenerator means and connected to and driving said indicator means fordriving said indicator means in response to the output of said pulsegenerator means;

. lockout means connected to said indicator means and to the input ofsaid pulse generator means, for locking out the operation of said pulsegenerator means for a fixed predetermined time period subsequent to eachpulse operation of said indicator means; and,

. power supply means connected to said indicator means, said switchmeans, said pulse generator means, said discriminator means, and saidnarrow bandpass amplifier means for energizing same.

2. The apparatus as described in claim 1 wherein said lockout meanscomprises a capacitor, a low time constant path through which saidcapacitor discharges when said switch means switches on said indicatormeans, a second and higher time constant path through which saidcapacitor charges when said switch means switches said indicator meansoff, and a normally open transistor switch connected in shuntingrelationship to the input of said pulse generator means and connected tosaid second path such that said pulse generator means is held inactivefor appreciably the time constant of said second path.

3. The apparatus as described in claim 1 wherein said pulse generatormeans comprises two transistors of opposite polarity, each having anoutput terminal, an input terminal, and a common terminal, a directcoupling resistance network connecting the output terminal of the firstof said transistors to the input terminal of said second transistor, asecond normally non-signal coupling network connecting the outputterminal of said second transistor to the input terminal of said firsttransistor, said second network containing a capacitor in series with asecond resistance network to provide a fixed time period of signalcoupling from the output terminal of said second transistor to the inputterminal of said first transistor.

4. The apparatus as described in claim 3 wherein each of said commonterminals is connected to a respective voltage reference, and each ofsaid input terminals is resistively con nected to its respective commonterminal, thereby maintaining each of said transistors non-conductingexcept when generating a pulse in response to a signal from saiddiscriminator means.

5. The apparatus as described in claim 41 wherein a diode is in serieswith the base-to-emitter junction of said first transistor, said seriescombination constituting said discriminator means.

6. The apparatus as described in claim 1 wherein said microphonetransducer means has a circular front housing and a rectangular backhousing, and has a trimming resistor in parallel with its outputterminals for standardizing the microphone output voltage.

7. The apparatus as described in claim 1 wherein an unregulated powersupply is connected to said indicator means, and a regulated powersupply is connected to said switch means, said pulse generator means,said discriminator means, and said narrow bandpass amplifier means.

and to turn off said first and second transistors after a predeterminedtime period, thereby providing a pulse output;

f. said discharge path resetting said combined circuit to a 8. In anelectronic instrument for amplifying a pulse train and for providing anindication of such pulses which exceed a predetermined lower limit inamplitude, a combined discriminator and pulse generator circuitcomprising:

a. a first diode, a first transistor with its base-to-emitter junctionin series with said first diode, both said diode and said junctionhaving forward bias voltages cooperating to provide a discriminatorturn-on voltage level;

b. a second transistor having an opposite polarity, and a resistivenetwork for connecting the collector of said first transistor to thebase of said second transistor;

c. a second diode, and a capacitor and first resistor in seriesconnected between the collector of said second transistor and the baseof said first transistor through said second diode, thereby providing afeedback path from the output of said second transistor to the input ofsaid first transistor;

. a third diode and a second resistor in series, connected to andproviding a discharge path for said capacitor;

. said capacitor having a charging path through said second diode andsaid first resistor, said charging path cooperating with said first andsecond transistors to turn on both said transistors when an inputvoltage in excess of said turn-on voltage is applied to the input ofsaid first diode condition to provide a next pulse output;

g. switch means connected to and driven by the output of said secondtransistor for providing a switchable output; and

h. lockout means connected to the output of said switch means and to theinput of said first transistor, for locking out the operation of saidcombined discriminator and pulse generator circuit for a fixedpre-determined time period subsequent to each of said pulse outputs.

9. The apparatus as described in claim 8 wherein said lockout meanscomprises a capacitor, a low time constant path through which saidcapacitor discharges when said switch means switches on, a second andhigher time constant path through which said capacitor charges when saidswitch means switches off, and a normally open transistor switchconnected in shunting relationship to the input of said first transistorand connected to said second path such that said first transistor isheld inactive for a second predetermined time period of about the timeconstant of said second path.

UNITED STATES PATENT OFFICE tE TIFIcA E or CORRECTION Patent No. 3,65l,798 Dated September 28 1972 Inventor(s) Paul H. Egli, et al I It iscertified that error appears in the above-identified patent and thatsaid Letters Patent are hereby corrected as shown below:

In the Title, after "NOISE", add -DI' SCRIMINATING PULSE AMPLIFIER.

Column 1, line 15, after "inflated", tshould be -to-.

Column 1, line 44, after "electronic";v delete -toand insert therefor-circuits-.

Signed and sealed this 3nd day of October 1972.

(SEAL) Attest:

EDWARD MQFLETCHERJRQ ROBERT GOTTSCHALK Attesting Officer v Commissionerof Patents USCOMM-DC 6O376-P69 ".5. GOVERNIIINT PRINTING OFNCE I969036-)34 "OHM PC4050 (10-69)

1. Blood pressure indicator apparatus for indicating the blood pressure of an individual by detecting auscultatory signals originating in the individual, said blood pressure indicator apparatus comprising: a. microphone transducer means, adapted to be placed against an arm of said individual, for generating electrical signals representative of blood flow sounds within said arm of said individual; b. narrow bandpass amplifier means having input terminals connected to the output terminals of said microphone transducer means for amplifying said representative signals, having filter sections providing for the amplification only of a narrow bandwidth of low frequency signals corresponding to the appreciable bandwidth of said blood flow signals; c. discriminator means connected to and driven by said amplifier means for providing output responsive only to signal amplitudes greater than a predetermined amplitude; d. pulse generator means connected to and driven by said discriminator means for providing output pulses of fixed amplitude and time duration responsive to the output signals of said discriminator means; e. indicator means for providing a visual output corresponding to the output pulses of said pulse generator means; f. switch means connected to and driven by the output of said pulse generator means and connected to and driving said indicator means for driving said indicator means in response to the output of said pulse generator means; g. lockout means connected to said indicator means and to the input of said pulse generator means, for locking out the operation of said pulse generator means for a fixed predetermined time period subsequent to each pulse operation of said indicator means; and, h. power supply means connected to said indicator means, said switch means, said pulse generator means, said discriminator means, and said narrow bandpass amplifier means for energizing same.
 2. The apparatus as described in claim 1 wherein said lockout means comprises a capacitor, a low time constant path through which said capacitor discharges when said switch means switches on said indicator means, a second and higher time constant path through which said capacitor charges when said switch means switches said indicator means off, and a normally open transistor switch connected in shunting relationship to the input of said pulse generator means and connected to said second path such that said pulse generator means is held inactive for appreciably the time constant of said second path.
 3. The apparatus as described in claim 1 wherein said pulse generator means comprises two transistors of opposite polarity, each having an output terminal, an input terminal, and a common terminal, a direct coupling resistance network connecting the output terminal of the first of said transistors to the input terminal of said second transistor, a second normally non-signal coupling network connecting the output terminal of said second transistor to the input terminal of said first transistor, said second network containing a capacitor in series with a second resistance network to provide a fixed time period of signal coupling from the output terminal of said second transistor to the input terminal of said first transistor.
 4. The apparatus as described in claim 3 wherein each of said common terminals is connected to a respective voltage reference, and each of said input terminals is resistively connected to its respective common terminal, thereby maintaining each of said transistors non-conducting except when generating a pulse in response to a signal from said discriminator means.
 5. The apparatus as described in claim 4 wherein a diode is in series with the base-to-emitter junction of said first transistor, said series combination constituting said discriminator means.
 6. The apparatus as described in claim 1 wherein said microphone transducer means has a circular front housing and a rectangular back housing, and has a trimming resistor in parallel with its output terminals for standardizing the microphone output voltage.
 7. The apparatus as described in claim 1 wherein an unregulated power supply is connected to said indicator means, and a regulated power supply is connected to said switch means, said pulse generator means, said discriminator means, and said narrow bandpass amplifier means.
 8. In an electronic instrument for amplifying a pulse train and for providing an indication of such pulses which exceed a predetermined lower limit in amplitude, a combined discriminator and pulse generator circuit comprising: a. a first diode, a first transistor with its base-to-emitter junction in series with said first diode, both said diode and said junction having forward bias voltages cooperating to provide a discriminator turn-on voltage level; b. a second transistor having an opposite polarity, and a resistive network for connecting the collector of said first transistor to the base of said second transistor; c. a second diode, and a capacitor and first resistor in series connected between the collector of said second transistor and the base of said first transistor through said second diode, thereby providing a feedback path from the output of said second transistor to the input of said first transistor; d. a third diode and a second resistor in series, connected to and providing a discharge path for said capacitor; e. said capacitor having a charging path through said second diode and said first resistor, said charging path cooperating with said first and second transistors to turn on both said transistors when an input voltage in excess of said turn-on voltage is applied to the input of said first diode and to turN off said first and second transistors after a predetermined time period, thereby providing a pulse output; f. said discharge path resetting said combined circuit to a condition to provide a next pulse output; g. switch means connected to and driven by the output of said second transistor for providing a switchable output; and h. lockout means connected to the output of said switch means and to the input of said first transistor, for locking out the operation of said combined discriminator and pulse generator circuit for a fixed pre-determined time period subsequent to each of said pulse outputs.
 9. The apparatus as described in claim 8 wherein said lockout means comprises a capacitor, a low time constant path through which said capacitor discharges when said switch means switches on, a second and higher time constant path through which said capacitor charges when said switch means switches off, and a normally open transistor switch connected in shunting relationship to the input of said first transistor and connected to said second path such that said first transistor is held inactive for a second predetermined time period of about the time constant of said second path. 